The present invention relates to a computer system and a method for controlling a computer system in which a plurality of operating systems (OS) operate on one computer, and in particular, to a computer system and a method for controlling a computer system in which computer resources can be efficiently used or operated in an operating state of a plurality of operating systems.
To improve reliability of computers, the JP-A-11-353292 describes a control technique of load distribution of the background art. The technique is called “cluster system” in which when an operating system running on a computer fails, another operating system receives processing of the failed operating system to continue the processing. In the system of the background art, at a failure of an operating system on a computer, programs running on the computer can be continuously executed.
To operate a plurality of operating systems in the cluster system which is a computer system of the background art, an equal number of computers and operating systems are required. The cluster system of the background art includes active computers and standby computers, and the active and standby computers operate independent of each other. In this connection, an active computer is a computer ordinarily operating, and a standby computer is a computer arranged to take over, when the active computer fails, processing of the failed computer to thereby continue the processing.
Therefore, in the cluster system of the background art, when a failure occurs on an active computer, processing thereof is passed to a standby computer. However, when a process is running on the standby computer, entire processing capability of the active computer cannot be achieved by the standby computer. In the background art system, while the standby system is kept stopped to take over the processing of the active computer, the computer resource of the standby computer cannot be efficiently used.
In a cluster system including, for example, two computers, one computer is an active system and the other one computer is a standby system. At occurrence of a failure in the active computer, when it is necessary that the standby computer achieves entire processing capability of the active computer failed, the standby computer must have processing capability at least equal to that of the failed computer. Moreover, at the failure in the active computer, the standby computer must stop processing being executed on the standby computer and then takes over processing from the failed computer to execute the processing. To execute the processing taken from the failed computer without stopping the own processing being executed by the standby computer, the standby computer must have processing capability higher than that of the failed computer.
Consequently, the cluster system of the background art is attended with a problem in which to achieve processing capability of one computer of the ordinary active system, there are required two computers each of which has processing capability equal to or more than that of the computer of the active system.